1. Field of the Invention
The present invention relates to a polarizing element, and in particular concerns an inorganic polarizing plate that is superior in durability with a superior transmitting characteristic over a wide range of wavelengths of light.
2. Description of the Related Art
It is indispensably required for a transmission type liquid crystal display apparatus to provide a polarizing plate on the surface of a liquid crystal panel from its image forming principle. The function of the polarizing plate is to absorb one of orthogonal polarized light components (so-called P-polarized light wave and S-polarized light wave) and also to transmit the other component. As the polarizing plate of this type, a dichroic polarizing plate formed by allowing a conventional film to contain an iodine-based polymeric organic substance and a dye-based polymeric organic substance has been widely used.
In recent years, the liquid crystal display apparatus has been expanded in its applications and has been highly functionalized. Accordingly, higher reliability and durability have been required for individual devices constituting the liquid crystal display apparatus. For example, in the case of a liquid crystal display apparatus using a light source with a large light quantum, such as, for example, a transmission-type liquid crystal projector, the polarizing plate is subjected to strong radiation. Therefore, the polarizing plate to be used therein needs to have superior heat resistance. However, since the above-mentioned film-based polarizing plate is an organic substance, it is inherently limited in increasing these characteristics.
In view of these problems, as the inorganic polarizing plate having superior heat resistance, various kinds of inorganic polarizing plates, such as a polarizing plate formed by dispersing silver fine particles in glass in an island pattern, a polarizing plate in which silver fine particles are deposited in glass, a polarizing plate using aluminum fine particles, and the like, have been proposed.
Moreover, a wire grid-type polarizing plate has been proposed in which metal thin wires are formed on a substrate with a pitch smaller than a wavelength of light within the used bandwidth so that a polarized light component that is in parallel with the metal thin wires is reflected, with an orthogonal polarized light component being transmitted, so that a predetermined polarizing characteristic is obtained, or a wire grid-type polarizing element has been proposed in which a dielectric layer and an inorganic fine particle layer are formed on a metal lattice so as to have three layers in total so that by cancelling light reflected from the metal lattice by the use of interference effect, a wire grid that is in general a reflection type is used as an absorption type, has been proposed (Patent Document 1: U.S. Pat. No. 4,488,033).
By the way, in the inorganic polarizing plate in which inorganic fine particles or an inorganic fine particle layer is formed, since its extinction ratio differs depending on the materials for the inorganic fine particles, in the inorganic polarizing plate, it is necessary to take into consideration to select inorganic fine particles that can provide a desired extinction ratio and to appropriately set the film thickness thereof, in order to reduce and optimize the reflectance in accordance with the bandwidth of light to be used.
An object of the present invention is to provide an inorganic polarizing plate that can reduce a reflectance by using a common structure even in the case when the wavelength bandwidth to be used is different, and to achieve a desired extinction ratio.